Typical multi-layered vacuum super insulated cryogenic tanks utilize a pair of cylindrical inner and outer tanks that are arranged concentrically with the inner tank residing in an interior of the outer tank. There are multiple radiant heat shields (insulation layers), approximately 30-80, coiled around the inner tank between the inner and outer tanks. A high vacuum exists between the inner and outer tanks to further prevent heat transfer. This type of thermal insulation is called a multi-layered vacuum super insulation. These storage tanks are capable of storing fluids at cryogenic temperatures.
The inner tank is positioned within the outer tank so that the inner tank does not contact the outer tank and so that thermal conduction paths between the inner and outer tanks are minimized. The fluid is supplied to and removed from the inner tank through a plurality of discrete fluid lines that extend through the outer tank, the vacuum between the inner and outer tanks, and into the inner tank at separate locations. Each of these fluid lines is a conductive heat path that can result in parasitic heat leaks into the inner tank.
The fluid lines are configured into an orientation that allows the fluid lines to extend between an interior of the inner tank and an exterior of the outer tank. Between the inner and outer tanks, the fluid lines are configured to raise or extend upwardly, to provide a favorable temperature profile from cold to warm, prior to passing through the outer tank. To minimize the conductive heat path formed by the fluid lines, the lines are spaced apart from the inner and outer tanks and are exterior to the insulation that is wrapped around the inner tank.
Current techniques for forming these cryogenic storage tanks utilize pre-bent metallic fluid lines. The pre-bent fluid lines are bent to an orientation that allows the fluid lines to extend between the inner and outer tanks without contacting either tank. These pre-bent lines, however, can interfere with the wrapping of the insulation layers around the inner tank. Specifically, the pre-bent lines can form multiple obstructions or interference locations with the applying of the insulation to the inner tank. These interferences increase the complexity of and/or eliminate the possibility of applying the insulation in an automated process.
Other types of cryogenic storage tanks utilize corrugated metal hoses or pipes for the fluid lines. The corrugation allows for the fluid lines to be easily and readily bent into a desired configuration. This enables the fluid pipes to be attached to the inner tank and bent subsequent to the application of the insulation layers. The use of fully-corrugated fluid lines, however, has disadvantages. For example, the fully-corrugated piping can expand or increase in length when the cryogenic storage tank is put into service. Specifically, the pressure differential between the interior and exterior of the fully-corrugated fluid lines can cause some elongation. The exterior of the fluid lines is exposed to the high vacuum that exists between the inner and outer tanks while the interior of the fully-corrugated fluid lines has pressurized fluid therein and may be on the order of 10-50 bars or greater. This pressure differential can cause the fully-corrugated fluid lines to expand and touch other parts and/or squeeze against the insulation. This can cause heat bridges between warm/cold parts and/or insulation layers, thus potentially increasing the heat influx into the fluid within the inner tank. Additionally, the fully-corrugated fluid lines are flexible and, as a result, fixation at both ends of the fully-corrugated fluid lines is not sufficient to fix their routing in place. Thus, when fully-corrugated fluid lines are used, additional supports, such as frames or brackets, are employed, thus requiring a further assembly step in the production of such fluid tanks.
Thus, it would be advantageous to provide a cryogenic storage tank and methods for manufacturing the same that avoid or reduce these disadvantages. It would further be advantageous if such a cryogenic storage tank and method of manufacturing same facilitated mass production of the storage tanks. The fluid lines are typically of a double wall construction inside the inner tank with a vacuum insulation therebetween to reduce the parasitic heat leaks into the inner tank. The double wall vacuum insulation shares the vacuum with the gap between the inner and outer tanks. This construction has various drawbacks. The use of discrete double wall fluid lines is labor intensive and makes automated production difficult. Additionally, the use of discrete double wall fluid lines results in multiple obstructions in the wrapping of the insulation layers around the exterior of the inner tank. The insulation layers need to be cut for each of these obstructions. Each of these cuts/breaks in the insulation layers results in a potential thermal shortcut for a parasitic heat leak into the inner tank. Furthermore, the cutting of the insulation layers is time consuming and makes automated production difficult. Thus, it would be advantageous to provide a storage tank that reduces or minimizes these drawbacks.